300–580 Nanometer Long-Slit Spectroscopy of Comet Tabur (C/1996 Q1)

Abstract

Comets Liller (C/1988 A1) and Tabur (C/1996 Q1) have similar orbits and are thought to have been a single comet until they split at a previous perihelion passage. Long-slit spectra of comet Tabur were obtained on consecutive nights around 45 days before perihelion. Nuclear production rate ratios for NH/CN, C3/CN, and C2/CN, determined from Haser model fits to the emission-line profiles, are consistent with a gas composition for comet Tabur identical with that measured by A'Hearn et al. for comet Liller. In a region between the photocenter and a projected position 5300 km sunward, the continuum light scattered from dust in the coma of comet Tabur was bluer than the light of solar-analog stars. Continuum flux in this region declined more steeply with projected distance from photocenter than is consistent with a uniform expansion. Farther sunward, the continuum was reddish with respect to solar analogs, while from the photocenter antisunward, it was neutral. The color profiles are similar in spectra obtained 24 hr apart, while the flux profiles differ. These data are difficult to explain by the action of solar radiation pressure on a population of long-lived grains of a single composition.